1. Field of the Invention
The present invention relates to a fuel supply control system for an internal combustion engine, and more particularly to a fuel supply control system for controlling a fuel supply amount in a period from startup to warm-up of the engine.
2. Description of the Prior Art
As a fuel supply amount calculating method suitable for the startup of the engine, a method in which a startup basic fuel amount is set according to a temperature of the engine coolant and the startup basic fuel amount is corrected according to the engine rotational speed is conventionally known. Further, a fuel supply amount calculating method suitable for after-startup of the engine (i.e., a method suitable for a condition after completion of the startup), is known in which a basic fuel amount is set according to the engine rotational speed and the intake pressure of the engine and the basic fuel amount is corrected by using various correction coefficients such as an increment correction coefficient set according to elapsed time after startup of the engine and a water temperature correction coefficient set according to the temperature of the engine coolant.
According to the conventional fuel supply control method, the fuel supply amount during startup of the engine is calculated according to the fuel supply amount calculating method suitable for the startup of the engine, and the fuel supply amount after startup is calculated according to the fuel supply amount calculating method suitable for after-startup of the engine, which is different from the method suitable for startup. The fuel supply amount calculating method is switched from the former to the latter upon completion of startup of the engine.
The above-described conventional fuel supply control method, however, has a problem in that it is difficult to allow the exhaust emission characteristic to fall within the exhaust emission regulation at an extremely low level by further reducing the emission amount of undesired components (particularly, an unburned HC component) in the exhaust gases.
Specifically, in order to reduce the emission amount of the unburned HC component emitted from the startup of the engine, it is required to realize optimal combustion by supplying an amount of fuel matched to an amount of intake air from the beginning of the startup. However, according to the conventional control method, the fuel supply amount cannot be controlled with the required accuracy because of the fact that during startup, the fuel supply amount is set only according to the engine temperature and the engine rotational speed, and at the time of completion of startup, the fuel supply amount having been set during startup is immediately changed to a fuel supply amount calculated by the fuel supply amount calculating method suitable for after-startup. Therefore, it is difficult to realize optimal combustion in a period from the startup to the warm-up of the engine.
Accordingly, an object of the present invention is to provide a fuel supply control system capable of improving the accuracy of control of a fuel supply amount in a period from startup to warm-up of the internal combustion engine, thereby allowing the exhaust emission characteristic to fall within an extremely low level exhaust emission regulation.
To achieve the above object, according to the present invention, there is provided a fuel supply control system for an internal combustion engine comprising startup fuel amount calculating means for calculating, during startup of the engine, a fuel amount to be supplied to the engine according to a fuel amount calculating method suitable for startup of the engine; after-startup fuel amount calculating means for calculating, after startup of the engine, a fuel amount to be supplied to the engine according to a fuel amount calculating method suitable for after-startup of the engine; and fuel supply means for supplying the fuel amount calculated by the startup fuel amount calculating means to the engine during startup of the engine, and supplying the fuel amount calculated by the after-startup fuel amount calculating means to the engine after startup of the engine. The fuel supply means includes transition control means for smoothly performing the transition from the fuel amount calculated by the startup fuel amount calculating means to the fuel amount calculated by the after-startup fuel amount calculating means.
With this configuration, during startup of the engine, a fuel amount is calculated by the fuel amount calculating method suitable for startup, and after startup of the engine, a fuel amount is calculated by the fuel amount calculating method suitable for after-startup, and the transition from the fuel amount calculated by the fuel amount calculating method suitable for startup to the fuel amount calculated by the fuel amount calculating method suitable for after-startup is smoothly performed. Accordingly, both during startup and after startup, the fuel amount suitable for each of the operating conditions is supplied to the engine, and the fuel supply amount is not rapidly changed upon completion of startup of the engine. As a result, it is possible to improve the accuracy of control of a fuel supply amount in a period from startup to warm-up of the engine, and hence to allow the exhaust emission characteristic to fall within an extremely low level exhaust emission regulation.
The transition control means smoothly, preferably performs the transition by correcting each of the fuel amount calculated by the startup fuel amount calculating means and the fuel amount calculated by the after-startup fuel amount calculating means, by using a transition coefficient varying with elapsed time.
With this configuration, since each of the fuel amount calculated by the fuel amount calculating method suitable for startup and the fuel amount calculated by the fuel amount calculating method suitable for after-startup is corrected by using the transition coefficient varying with elapsed time, the transition of the fuel amount can be smoothly performed, and the manner of the transition control can be easily altered by changing the transition coefficient.
The transition coefficient is preferably set according to the number of combustions (e.g. the generated number of TDC signal pulses) in the engine. Alternatively, the transition coefficient may be set according to a count value of a timer.
Preferably, the startup fuel amount calculating means and the after-startup fuel amount calculating means respectively include startup adhesion correcting means and after-startup adhesion correcting means for correcting a delay in transfer of fuel due to adhesion of part of the fuel injected into the intake pipe of the engine, to an inner wall of the intake pipe. The startup adhesion correcting means corrects the fuel amount by using startup adhesion correction parameters and the after-startup adhesion correcting means correcting the fuel amount by using after-starup adhesion correction parameters which are set independently from the startup adhesion correction parameters. The transition control means smoothly performs the transition from the startup adhesion correction parameters to the after-startup adhesion correction parameters by correcting the startup adhesion correction parameters and the after-startup adhesion correction parameters by using a transition coefficient varying with elapsed time.
With this configuration, the fuel amount is corrected during startup by using the startup adhesion correction parameters and the fuel amount is corrected after startup by using the after-startup adhesion correction parameters, and the transition from the startup adhesion correction parameters to the after-startup adhesion correction parameters is smoothly performed by correcting each of the startup adhesion correction parameters and the after-startup adhesion correction parameters by using the transition coefficient varying with elapsed time. Accordingly, both during startup and after startup, the adhesion correction suitable for each of the operating conditions is performed, and the adhesion correction parameters are not rapidly changed upon completion of startup. As a result, it is possible to more accurately control the fuel supply amount in consideration of the fuel adhering to the inner wall of the intake pipe of the engine.
The transition control means preferably sets the transition coefficient according to a temperature of the engine.
With this configuration, the transition coefficient used for the transition control of the transition from the fuel amount calculated according to the fuel amount calculating method suitable for startup to the fuel amount calculated according to the fuel amount calculating method suitable for after-startup is set according to the engine temperature. Accordingly, the rate or the termination time of the transition from the fuel amount calculated according to the fuel amount calculating method suitable for startup to the fuel amount calculated according to the fuel amount calculating method suitable for after-startup changes depending on the engine temperature. As a result, it is possible to perform the transition control optimally adapted to the engine temperature during startup.
The transition control means preferably sets the transition coefficient so that the transition rate becomes faster as the temperature of the engine becomes higher.
The transition control means preferably sets the transition coefficient so that the completion timing of the transition becomes earlier as the temperature of the engine becomes higher.
Preferably, the startup fuel amount calculating means calculates a modified startup basic fuel amount by correcting a startup basic fuel amount set according to the engine rotational speed and the intake pressure by using at least one of a startup intake air temperature correction coefficient set according to the intake air temperature, a startup atmospheric pressure correction coefficient set according to atmospheric pressure, and a startup engine temperature correction coefficient set according to the engine temperature, and calculates the fuel amount to be supplied to the engine during startup by using the modified startup basic fuel amount; and the after-startup fuel amount calculating means calculates a modified after-startup basic fuel amount by correcting an after-startup basic fuel amount set according to the engine rotational speed and the intake pressure by using at least one of an after-startup intake air temperature correction coefficient set according to the intake air temperature, an after-startup atmospheric pressure correction coefficient set according to atmospheric pressure, and an after-startup engine temperature correction coefficient set according to the engine temperature, and calculates the fuel amount to be supplied to the engine after startup by using the modified after-startup basic fuel amount.
The transition control means preferably, smoothly performs the transition from the modified startup basic fuel amount to the modified after-startup basic fuel amount by using a transition coefficient varying with elapsed time.
Other objects and features of the invention will be more fully understood from the following detailed description and appended claims when taken with the accompanying drawings.